P0420 How To Diagnose A Bad Catalytic Converter -EricTheCarGuy

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O2 Sensor Video: https://www.youtube.com/watch?v=NIzcz...

Discussion about this video: http://www.ericthecarguy.com/forum/18...

I know this video will not only save people some money but also I think it will solve a lot of confusion concerning the operation of the catalytic converter. These tests work as you can see in the video. So the next time you have a P0420 or someone tells you your catalytic converter is bad you'll know what to do to find out if that is indeed the case.

Stay dirty

ETCG

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Closed Caption:

greetings viewers Eric our guy here back
again with another video for you this
one not necessarily repair video but
something informational what we want to
talk about today is how do you know if
your catalytic converter is bad
all over my foreign people are asking I
think my catalytic converters bad
and let's face it catalytic converters
are really expensive in some cases
sometimes in the thousands of dollars
and you really want to be sure that it
is bad before you replace it
some say that you may be able to clean
catalytic converters
honestly I've never tried it so I can't
say one way or another whether that's
going to be something that's going to
work for you or not
honestly you're gonna have to try that
yourself but what i thought i would do
is i thought i'd give you a quick
rundown on basically a couple of quick
test that you can perform to determine
if your catalytic converter is doing his
job
i'm going to be using two tools in
particular one a cheap infrared
thermometer into a bi-directional scan
tool that can read live data
let's start with the easy stuff by
getting the bi-directional scan tool
with live data and let's use that method
first I'm going to first start by
plugging in my bi-directional scan tool
which in the case of the subaru goes in
up underneath the dash here and I'm
gonna have to start run the vehicle but
i think it's worth at least talking
about the job or function of the
catalytic converter before we go much
further
catalytic converter is basically there
to reduce nox emissions and what that is
is nitrogen combines with oxygen and
there's it's really not determine how
many oxygen molecules combine with the
nitrogen molecules
that's why there's an X instead of a
number like h2o is two hydrogen atoms
and one oxygen atom
whereas Knox is no X and that X could be
any number of oxygen atoms that combined
with nitrogen the bad stuff it's
basically stuff that creates the smog
so they put these really expensive
things on the exhaust system to try to
clean up these nox emissions and
basically what the catalytic converter
does is it gets really hot like an oven
that's that's what it's supposed to do
with it
functions best and i think it's like
1300 degrees twelve thirteen hundred
degrees fahrenheit i'm not sure what
that is Celsius sorry
and what it does is it takes that those
nitrogen molecules and those oxygen
molecules and breaks them apart
so in essence you want your catalytic
converter to get hot like an oven and
that and that's basically what we're
testing for here so we're going to
monitor the efficiency using the o2
sensors and this will only work and
vehicles that are post 96 vehicles
before 1996 didn't require an o2 sensor
to be in the catalytic converter or any
catalyst monitoring within those those
fuel system strategies
so you wouldn't necessarily be able to
do this test however you would be able
to do my other tests with the infrared
thermometer so we'll start the vehicle
up and number one thing we got to get it
up to temperatures so we're gonna have
to run this for a little while
get it up to temperature first they have
gotten up to temperature and these are
the readings that i'm getting i made
myself a custom data list and i set it
up to where we've got coolant
temperature the primary o2 sensor and
the secondary o2 sensor so what I'm
going to do now is I'm gonna raise the
RPMs to about 2,000 rpm somewhere
between 2000 2500 should be good just to
make sure that the catalytic converters
hot enough to do anything and then we'll
observe these readings
ok now I'm kind of seeing what I don't
want to see here and that is what i'm
looking for is I want my secondary o2
sensor to pretty much stay steady right
around a half of volt and I want my
primary o2 sensor to switch back and
forth rapidly rich lean that would
indicate that my primary to is working
like it should and my catalyst is
working like it should
what kind of as you can see here what
I've got is I've got a secondary OH -
that's actually kind of switching all
over the place rather rapidly back and
forth across rich and lean so this kind
of says that that my catalytic
converters in the subaru here are really
doing their job and just just to be
clear on this Subaru there's actually
two catalytic converters
there's one that's right by the engine
and then about a foot back from that
there's another one
they only have 1 o2 sensor in the
secondary catalytic converter so they
don't truly take a reading of the
efficiency of the of the first catalytic
converter they're just taking a reading
of both sort of as a general thing if if
you do when i'm doing here and you're
seeing this these types of readings
there's a good chance that that your
catalytic converter is not doing its job
in fact I would say that this vehicle
might fail emissions due to do - knocks
because of what I'm seeing here
let's go for the second test and and
actually check the catalytic converters
temperature just to see what we got
here we are under the Subaru
probably not hear me so great because
the engine running
I've got the engine running at about
that 2000rpm that we talked about a
happy
read thermometer here
take the test
catalytic converter bolts at the inlet
and the out
says with the
the seal
really this catalytic
murder is not working like it should
let's try the one
back
this one's not working like it's
supposed to either
ok I'm busted well here in Ohio we don't
have emissions testing anymore so i
guess i'm good and I can still drive
along
however if i were to have to replace
those catalytic converters I would
imagine it would be pretty expensive and
i would also say that this vehicle would
probably fail for nox emissions and i'm
sure you'd love to see what a good
catalytic converter does so why don't we
do that for you right now
okay well it was kind of obvious that
the subaru failed so i'm now in my
Odyssey looking at the exact same
numbers so and up and I'm also keeping
the RPMs like around 2,500 2010 a little
bit
and here's what our numbers are we up to
operating temperature and you can see
the secondary o2 sensor is pretty much
stayed around that half a volt mark
where I said that you kind of wanted to
see and plus it's slow it's not moving
really rapidly but you can see the
primary o2 sensor is switching really
fast up and down over half a volt so the
primary o2 sensors doing this job it's
checking fuel trip and the secondary 02
is just kind of hanging out there
this means that this catalytic converter
is working like it should
so this is kind of what you want to see
not a whole lot of switching on the
secondary but plenty of switching on the
primary now let's check his temperature
and see if that proves out also
under the odyssey and i'm going to try
to sleep
30 degrees here in
well that was quite a learning
experience wasn't it we got a chance to
look at catalytic converters that were
working like they should
and a catalytic converter that is
working like it should and as I said and
you can see on the odyssey clearly how
the secondary o2 sensor was kind of just
hanging out at a given voltage where the
primary o2 sensor was switching back and
forth pretty rapidly
that's what you want to see unlike the
subaru where we were looking at that and
you could see that the secondary o2
sensor was going a little more quickly
and also the temperature the temperature
was actually a hundred three hundred
degrees colder on the subaru at the
outlet the inlet as opposed to the
odyssey which was indeed about a hundred
degrees hotter at the outlet than it was
at the inlet indicating that it was
doing what it was supposed to do
so you have a thermometer and a
bi-directional scan tool which can tell
you this information and possibly save
you thousands of dollars
whether or not you really need a
catalytic converter or not
yes you can't rule out the possibility
that it's an o2 sensor problem but in my
experience many times if you've got
appeal for 20 code
normally that's what you're going to see
you're going to look at those 02
readings and you'll see that the primary
and secondary or switching fairly
rapidly together are close to it and you
also if you go to take the temperature
you'll find that it's actually possibly
colder at the outlet and then at the
inlet
anyway I American car guy I hope this
information was helpful to you
you can always find me over at the car
guy . com where I asked you go and
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have fun and stay dirty and keep your
tail pipes or at least your emissions
clean